Heat treatment method of unleaded brass alloy

ABSTRACT

A heat treatment method for unleaded brass alloy is provided to improve processability, cracking resistance, wear resistance and anti-corrosive property of unleaded brass alloy containing no lead or containing a very small amount of lead. The heat treatment method includes full annealing an unleaded brass alloy material, mechanical processing the material after full annealing and soft annealing the material after mechanical processing.

FIELD OF THE INVENTION

The present disclosure relates to a heat treatment method for unleaded brass alloy. More particularly, the present disclosure relates to a heat treatment method for unleaded brass alloy, intended to improve processability, cracking resistance, wear resistance and anti-corrosive property of unleaded brass alloy containing no lead or containing a very small amount of lead.

BACKGROUND OF THE INVENTION

In general, copper alloy is used widely in automobile parts, electronic parts, piping members (faucet metallic parts, valves, etc.), or the like, and is required to have excellent mechanical processability and anti-corrosive (anti-dezincification) property with time.

It is known that addition of lead is effective for improving mechanical processability and anti-corrosive (anti-dezincification) property of copper alloy.

When preparing lead-containing copper alloy, several dangerous factors always exist since such alloy contains lead that adversely affects the human body and environment. For example, workers may inhale lead components in metal vapor generated during dissolution or casting of alloy. In addition, in the case of a piping member using brass alloy as a main component, lead components may be dissolved out by the contact with drinking water and absorbed by the human body.

Meanwhile, brass alloy (unleaded brass alloy) containing no lead that adversely affects the human body and environment may show poor mechanical processability. Therefore, as a typical example of unleaded machinable alloy containing no lead or cadmium, Japanese Patent Application Publication No. 2000-119775 discloses copper alloy having a tensile strength of 600-800 MPa. Although such alloy provides copper alloy with improved mechanical processability (machinability) through the use of a silicon (Si) additive, it shows larger cutting resistance than lead-containing brass alloy because Si is softer than copper or lead, and tools using such alloy have low service life.

In addition, unleaded brass alloy itself has poor processability, and thus the alloy is merely applied to casting. Therefore, the alloy as-produced may not be applied to some products, such as piping fittings, required to be processed into various shapes.

To realize excellent mechanical properties, another type of alloy has been obtained by doping an element that has improved mechanical processability while substituting for lead or cadmium capable of adversely affecting the human body or environment. For example, such a type of alloy may be one containing bismuth (Bi), etc. and having a different compositional ratio of brass alloy. However, since bismuth is expensive and causes cracking during low-temperature processing due to its brittleness, production of articles using such bismuth-containing alloy is not cost-efficient and the resultant articles are limited in application.

SUMMARY OF THE INVENTION

The present disclosure is directed to providing a heat treatment method for unleaded brass alloy, which realizes excellent mechanical processability, anti-corrosive property and wear resistance, and improves cracking with time without adding any ingredient for improving processability, wherein the brass alloy containing no lead harmful to the human body or environment or containing such a small amount of lead that does not adversely affecting the human body or environment.

In one aspect, there is provided a heat treatment method for unleaded brass alloy, including:

full annealing an unleaded brass alloy material to remove internal stress and boundary cracking;

mechanical processing the material after fully annealing; and

soft annealing the material after mechanical processing to remove stress concentration caused by mechanical processing and residual stress.

In another aspect, there is provided a heat treatment method for unleaded brass alloy, including:

forging an unleaded brass alloy material;

full annealing the material after forging to remove stress and boundary cracking caused by external force applied during the heating and forging of the material;

mechanical processing the material after fully annealing; and

soft annealing the material after mechanical processing to remove stress concentration caused by mechanical processing and residual stress.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the disclosed exemplary embodiments will be more apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram illustrating the heat treatment method according to an embodiment;

FIG. 2 is a block diagram illustrating the heat treatment method according to another embodiment;

FIG. 3 shows photos illustrating the structure of a fully annealed unleaded brass alloy material as compared to that of non-annealed unleaded brass alloy material; and

FIG. 4 shows a table of test results for a piping fitting specimen after carrying out the heat treatment method partially or completely in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown.

As used herein, the term ‘unleaded brass alloy’ means brass alloy containing no lead or containing a very small amount of lead.

In the following embodiments, naval brass may be used as an unleaded brass alloy material.

FIG. 1 is a diagram illustrating the heat treatment method according to an embodiment. As shown in FIG. 1, the heat treatment method includes an operation S1 of full annealing an unleaded brass alloy material, an operation S2 of mechanical processing the material after the operation S1, and an operation S3 of soft annealing the material after the operation S2.

In the operation S1, the material is subjected to full annealing at a temperature of 530±30° C. for 3 hours. Such full annealing improves the mechanical processability of the material and removes boundary cracking caused by stress concentration.

The mechanical processing operation S2 includes, for example, processing the brass alloy into a desired piping fitting.

Then, in the operation S3, soft annealing is carried out at a temperature of 330±30° C. for 1 hour. Such a final soft annealing operation removes the internal stress of the processed material (piping fitting) to prevent cracking and to improve wear resistance and anti-corrosive property.

As shown in FIG. 2, the heat treatment method according to another embodiment of the present disclosure includes an operation P1 of forging an unleaded brass alloy material, an operation P2 of full annealing the material after the operation P1, an operation P3 of mechanical processing the material after the operation P2, and an operation P4 of soft annealing the material after the operation P3.

In other words, the material (C46400) is not subjected directly to heat treatment (annealing) but subjected to forging first. After the forging, the forged brass alloy is fully annealed. Next, the fully annealed brass alloy is subjected to mechanical processing, and then the processed brass alloy is further subjected to soft annealing so that the forged product has a stable structure.

In a similar manner to Embodiment 1, the forged product is subjected to full annealing P2 at a temperature of 530±30° C. for 3 hours. Such full annealing improves the mechanical processability of the material and removes stress and boundary cracking caused by external force applied during the heating and forging.

In addition, the operation P4 of soft annealing is carried out at a temperature of 330±30° C. for 1 hour. In this manner, stress concentration caused by mechanical processing and residual stress are removed, thereby preventing cracking and improving wear resistance and anti-corrosive property.

After carrying out full annealing or soft annealing under the above-defined temperature and time conditions in nitrogen gas atmosphere according to the heat treatment method disclosed herein, cracking with time and dezincificative corrosion that may be generated in metal structures after forging and mechanical processing are prevented.

If the heat treatment is carried out not in nitrogen gas atmosphere but in ambient atmosphere, corrosion may occur due to gases, such as oxygen and ammonia, and surface hardening may occur as the surface corrosion proceeds. Therefore, the heat treatment is carried out in nitrogen atmosphere in order to prevent corrosion.

FIG. 3 shows the product heat treated according to an embodiment as compared to non-heat treated product.

As shown in FIG. 3, the raw material shows a high degree of corrosion before full annealing, while it shows a relatively low corrosion after full annealing.

In other words, as corrosion proceeds, the raw material structure shows a high degree of splitting. After annealing, splitting is decreased as compared to the same material before annealing. This suggests that the heat treatment method disclosed herein improves the anti-corrosive property of the material.

FIG. 4 is a table showing the test results for three kinds of piping fitting specimens (total 6 specimens, including 1, 1-1, 2, 2-1, 3, 3-1). As can be seen from the magnified view, specimens 1-1, 2-1 and 3-1 heat treated according to the heat treatment method disclosed herein show a relatively lower degree of cracking with time and corrosion, as compared to specimens 1, 2 and 3.

Specimen 1 is the same type of piping fitting as specimen 1-1, specimen 2 is the same as specimen 2-1 and specimen 3 is the same as specimen 3-1, except that they are subjected to different heat treatment methods.

Meanwhile, the heat treatment method disclosed herein may be applied not only to unleaded brass alloy containing no lead, but also to unleaded brass alloy (C46400 series) containing such a small amount (0.005-0.2 wt % based on the total weight 100 wt %) of lead that does not adversely affect the human body and environment, so that the brass alloy may realize improved mechanical processability and anti-corrosive property.

As can be seen from the foregoing, there is provided a heat treatment method for unleaded brass alloy containing no lead or containing a very small amount of lead. According to the heat treatment method, it is possible to use unleaded brass alloy as an eco-friendly material, to improve mechanical processability, wear resistance, structural uniformity, cracking resistance and anti-corrosive property, and thus to prevent cracking and dezincificative corrosion on the surfaces of processed articles with time. As a result, the unleaded brass alloy may be used suitably in piping fittings for drinking water, or the like.

While the present disclosure has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the disclosure as defined in the following claims. 

1. A heat treatment method for unleaded brass alloy, comprising: full annealing an unleaded brass alloy material; mechanical processing the material after full annealing; and soft annealing the material after mechanical processing, wherein the full annealing is carried out at a temperature of 530±30° C. and the soft annealing is carried out at a temperature of 330±30° C.; and the unleaded brass alloy material contains lead in an amount of 0.2 wt % or less.
 2. The heat treatment method according to claim 1, wherein the unleaded brass alloy material is naval brass.
 3. The heat treatment method according to claim 1, wherein the full annealing is carried out for 3 hours.
 4. The heat treatment method according to claim 1, wherein the soft annealing is carried out for 1 hour.
 5. The heat treatment method according to claim 1, wherein the full annealing or the soft annealing is carried out in nitrogen atmosphere.
 6. (canceled)
 7. A heat treatment method for unleaded brass alloy, comprising: forging an unleaded brass alloy material; full annealing the material after forging; mechanical processing the material after full annealing; and soft annealing the material after mechanical processing; wherein the full annealing is carried out at a temperature of 530±30° C.; and the soft annealing is carried out at a temperature of 330±30° C., and the unleaded brass alloy material contains lead in an amount of 0.2 wt % or less.
 8. The heat treatment method according to claim 7, wherein the unleaded brass alloy material is naval brass.
 9. The heat treatment method according to claim 7, wherein the full annealing is carried out for 3 hours.
 10. The heat treatment method according to claim 7, wherein the soft annealing is carried out for 1 hour.
 11. The heat treatment method according to claim 7, wherein the full annealing or the soft annealing is carried out in nitrogen atmosphere.
 12. (canceled) 